This document discusses charging and discharging of capacitors. It defines a capacitor as a device that stores electric charge, consisting of two metal plates separated by an insulator. When a charged capacitor is connected to a battery, electrons flow from the battery charging the capacitor plates until the potential difference equals the battery voltage. The rate of charging decreases over time according to an exponential relationship defined by the time constant, which is the product of the capacitor's resistance and capacitance. When fully charged, the energy stored in the capacitor is equal to one-half of the maximum voltage squared multiplied by the capacitance. During discharging, the stored charge leaves the capacitor through the external circuit, also following an exponential relationship defined by the time constant.

1. GUJARAT TECHNOLOGICAL UNIVERSITY
BIRLA VISHVAKARMAMAHAVIDYALAYA
(ENGINEERING COLLEGE)
VALLABH VIDYANAGAR
SUBJECT: ELEMENTS OF ELECTRICAL ENGINEERING
(CODE-2110005)
BE First Level Second Semester (Self Finance)
Topic : Charging and discharging of capacitors

2. Capacitors
• A capacitor is a device for storing electric
charge.
• It can be any device which can store charges.
• Basically, capacitors consists of two metal
plates separated by an insulator. The insulator
is called dielectric. (e.g. polystyrene, oil or air)
• Circuit symbol:
+
_
Dielectric

3. Circuit of process charging and
discharging

4. Charging of capacitors
• When a capacitor is connected across a battery, electrons flow
from the negative terminal of the battery to a plate of the
capacitor connected to it. At the same rate, electrons flow
from the other plate of the capacitor to the positive terminal
of the battery. This gives a flow of current as the capacitor is
being charged.
• As charges accumulate on the plates of the capacitor, electric
potential built across the plates. This hinders further
accumulation of charges and makes the charge up current
decreasing. When the potential difference across the plates
equals that of the battery, the current becomes zero.

5. Charging a Capacitor
• Voltage-charge
characteristics
• Current flow
I
t
Vc
or Q
t
)1(0
RC
t
C eVV


RC
t
oeII


Vc ∝ Q

6. FORMULA FOR CHARGING
PROCESS
a. Time constant , ‫ג‬ = CR
b. Initial Charging current
I max = V/R
c. Charging voltage of capacitor,
Vc = Vmax (1 – e -t/‫ג‬ )
d. Charging current
i = Imax (e -t/‫ג‬ )

7. e. Initial rate of change potential
difference
dVc = V / CR
dt
f. Time when capacitor fully charge
t = 5‫ג‬
g. Energy stored, E = ½ CVmax2

8. Discharging a Capacitor
• Voltage-charge
characteristics
• Current flow
VC
or Q
t
I
t
RC
t
eQQ

 0
RC
t
oeII



9. Formula for discharging process
a. Time constant , ‫ג‬ = CR
b. Initial disharging current
I max = V/R
c. Disharging voltage of capacitor,Vc = Vmax (
e -t/‫ג‬ )
d. Discharging current
i = - Imax (e -t/‫ג‬ )

10. e. Initial rate of change
potential difference
dVc = V / CR
dt
f. Time when capacitor decrease
charge
t = 5‫ג‬

11. Prepared by :
Kakadiya Krushal (Production) – 130080125006
Mehul Ghodasara (Mechanical) – 130080119008
Milind Bhoya (Mechanical) – 130080119004

12. Thank you